Tfl 505 
.U7 
1917 
Copy 1 



EPAETMEITT OF COMMEEOE 

U. S. COAST AND GEODETIC SURVEY 
E. LESTER JONES, Supeeintendent 



HYPSOMETRY 



USE OF MEAN SEA LEVEL AS THE DATUM 
FOR ELEVATIONS , 



BY 



E. LESTEE JONES 

SUPERINTENDENT 



Special Publication No. 41 




PRICE, 5 CENTS 

ii .. Sold only by the Superintendent of Documents, Government Printing Office Washington, D. ' 




WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1917 



Monograph 



n 



Serial No. 60 



DEPAETME]^T OF COMMEKOE 

U. S, COAST AND GEODETIC SURVEY 

E. LESTER JONES, Superintendent 



HYPSOMETRY 



USE OF MEAN SEA LEVEL AS THE DATUM 
FOR ELEVATIONS 



BY 



E. LESTER JONES 



SUPERINTENDENT 



Special Publication No. 41 




PRICE, 5 CENTS 

Sold only by the Superintendent of Documcni-s, Government Printing Oflicc Washington, D. C. 



WASHINGTON 
GOVERNMENT PRINTING OFFICE 
1017 • 



\( 



c> 






D. of D. 
JUL IS 1917 







USE OF MEAN SEA LEVEL AS THE DATUM FOR ELEVATIONS. 



By E. Lester Jones, Superintendent. 



The term " engineering " is usually considered to be synonymous 
with the word " efficiency," but in at least one branch of engineering 
it is only partly true. This is in leveling. 

There is scarcely any surveying or civil engineering which does not 
require that differences in elevation be determined by spirit leveling, 
and in nearly all cases the absolute elevation of the bench marks 
above some plane of reference or datum is determined. Efficiency in 
operation and in the results frequently depends upon the datum 
selected. 

What is a satisfactory datum? This is a very important question 
and one to which much thought is directed by engineers. If one is 
grading streets or extending a sewerage or water system in a city, it 
is evident that the official city datum should be used in the leveling 
operations; but if a city is to adopt a surface for its datum, what 
should it be? Evidently it should adopt that datum which is most 
generally used by State engineering departments, by the railroads 
which enter it, and by other engineering organizations. 

Then the State itself must consider what datum it should adopt, 
and its decision should be based upon the previous decision of other 
States adjoining it. 

Finally, what datum should the Nation adopt ? It is evident that 
it would be impracticable for the Nation, especially one of 3,000,000 
square miles of area, as is the case in the United States, to adopt the 
surface through some one bench mark as its datum in its early engi- 
neering work, for this would require that an elaborate system of 
levels should precede all its surveying and engineering operations. 

Only slight consideration leads one to conclude that the ideal 
datum for a nation is one which may be established at many places. 
The only one of this kind is mean sea level. 

Mean sea level is that surface which would be assumed by the sur- 
face of the water of the ocean if it were not disturbed by the attrac- 
tion of the sun and moon and the force of the wind. 



4 UNITED STATES COAST AND GEODETIC SURVEY. 

Mean sea level may be established within a very small fraction of 
a foot by continuous tidal observations for at least a year. It has 
been found from precise-leveling observations that mean sea level, 
as established at different points on the open coasts, is at all such 
points in the same equipotential surface; that is, if there were no 
resistance of the water and wind to the movement of an object float- 
ing on the ocean the object could be moved from one point on the 
coast to another without performing any work — there would be no 
lifting necessary. 

While this statement may not be absolutely true, yet it is so nearly 
the case that for all engineering and surveying purposes it may be 
accepted as rigidlj^ true. 

If we have a surface at hand which makes an ideal datum for the 
elevations of the country, should it be adopted ? Efficiency demands 
that it should be. 

Mean sea level is now used exclusively as the datum for all surveys 
on land by the Coast and Geodetic Survey and by the United States 
Geological Survey. It is only occasionally used by the Engineering 
Corps of the Army and not always by the Reclamation Service. 

Usually the General Land Office does no leveling in connection 
Ayith its surveys of the public lands. There is no other Federal 
organization which covers large areas in its surveying work. 

We can scarcely say, in consideration of the evidence, that mean 
sea level has been universally adopted by the Federal Government as 
the datum for all of its elevations. 

In December, 1916, the Coast and Geodetic Survey sent the follow- 
ing letter, or one similar to it, to the chief engineers of most of the 
large cities of the country, to the State engineer of each State, and 
to the chief engineer of each of about 150 railroads in the United 
States: 

As you know, one of the important operations of tlie United States Coast and 
Geodetic Survey is the extension over the country of a networli of precise level- 
ing which will give elevations of great accuracy, based upon mean sea level. 

We believe that this precise leveling is essential in the surveying and engi- 
neering work done in this country by various public and private agencies. The 
network will enable engineers to use the sea-level datum on new projects and 
to reduce to this datum existing elevations referred to arbitrary datums. We 
believe that this country should eventually have but one datum, in order that 
all engineering and surveying work may be easily coordinated. We believe 
also that the presence of various datums leads to much confusion and waste. 

In order that we may get into closer touch with the needs of the engineering 
profession, I should be glad if you will let me know to what extent your State 
is basing the elevations of its road and other surveys and engineering works 
upon mean sea level; also whether the use of various arbitrary datums by 
counties, cities, and private organizations within your State is a serious matter 
in the industrial development of your St.-ite, 

Replies were received from many of these engmeers. 



MEAN SEA-LEYEL DATUM FOB ELEVATIONS. 5 

The engineers of five of the cities, namely. Fort Worth and El 
Paso, Tex., Ponghkeepsie, N. Y., Birmingham, Ala., and Terre 
Haute, Ind., reported that mean sea level had been adopted as the 
official datum for all elevations used by those cities. It was known 
that Cincinnati had adopted mean sea level as its official datum 
some years ago. 

The engineers of most of the cities reported that arbitrary datums 
had been in use for many years. Many of them stated that it was 
generally realized that mean sea level should be used as the official 
datum, but that the expense incident to changing the many ordi- 
nances, profiles, plates, etc., made its adoption of doubtful expe- 
diency. There are given later extracts from some of the city engi- 
neers' replies. (See pp. 6 to 8.) 

Responses were received from most of the State engineers, some 
of them signing as State highway engineer, others as director of the 
State Geological Survey, engineering commissioner, etc. In all cases 
except one, the State engineer informed the Bureau that mean sea 
level vras used as the datum for the State work wherever bench 
marks were available whose elevations were based on this datum. 
They strongly advocated the rapid extension of the precise-leveling 
system of the country in order that no extensive engineering and sur- 
ve,ying should have to be based upon assumed elevations or ar- 
bitrary datums. 

Extracts from the letters of some of the State engineers are given 
on pages 9 to 12. They show very clearly and strongly the de- 
sirability of having a single datum for the country. 

The chief engineers of many of the railroads replied to the in- 
quiries of the Survey and, in nearly all cases, they stated that mean 
sea level was used, or was in process of adoption, by their roads. 
The general expression of opinion was that the precise-leveling net of 
the countr}^ should be completed or greatly extended in order that 
the accurate elevations might be at hand as the base for what might 
be termed the " detailed leveling." 

Instances were cited where a road had apparently been on 
sea-level datum, but considerable error had been disclosed after the 
precise leveling had been extended to its lines. Such instances as 
these show that mean sea -level elevations in areas far from the coasts, 
if not based upon precise levels, may be in error to such an extent 
that for practical purposes they may be considered as being based 
upon arbitrary datums. 

Extracts from letters of some of the chief engineers of railroads 
are given on pages 13 to 18. 

The city engineer of Terre Haute, Ind., stated that sea -level 
datum was in use m his city and that he found the use of the United 



6 UNITED STATES COAST AND GEODETIC SURVEY. 

States Government bench marks of great benefit to him. He thought 
that the Government should have bench marks in all cities of at least 
25,000 population and that it would be of great benefit if the Gov- 
ernment established bench marks in even smaller cities. 

The city engineer of Fort Worth, Tex., wrote this Office in part as 
follows : 

The elevations of our bench marks throughout Fort Worth have been changed 
to conform to the datum established by the Coast and Geodetic Survey. We 
have extended these bench marks to cover the entire town. I consider the ex- 
tension of your level nets of the greatest importance to the country. Having 
some definite datum to work from has been a great convenience and benefit to us. 

The city engineer of Detroit, Mich., stated that in his city the 
official datum is an arbitrary one, but that the relation between the 
city datum and mean sea level had been established. He added : 

I can see no objection to the city adopting the Government datum as estab- 
lished here. Of course there are a great many records throughout the city, 
both public and private, that would be affected, but I think it would be wise to 
make the change. 

The chief engineer of the Topographical Sur \^ey Commission of the 
City of Baltimore wrote this office, in part, as follows : 

The city of Baltimore in 1893 established a series of precise-level bench 
marks which have been used since that time in connection with all engineering 
work carried on by the municipality. This survey has for its datum the mean 
low^ tide at Baltimore. 

The Pennsylvania Railroad, as well as other organizations, used still a dif- 
ferent datum, so one can see that, although the city's precise-level work has 
been carried out to a degree of precision equal to that adopted by your survey 
and is satisfactory for all city work, it would have been much better if the 
datum adopted for Baltimore had been that of mean sea level. This, I am sure, 
would have been done if at the time this survey was started a Government 
bench mark had been available. This would, to a certain extent, have done 
away with certain confusions which now exist. 

We believe that the plan for the United States Government to establish bench 
marks throughout the country, based on mean sea-level datum, would en- 
courage the use of that datum by all who wish to carry on any extensive 
system of leveling, and would prove a great convenience and eliminate many 
errors and much confusion. 

The city engineer of Duluth, Minn., wrote that Duluth had adopted 
mean level of Lake Superior as its datum. He stated : 

The only objection to making the change to sea-level datum would be the 
altering of our records, but other than that it would be a good move to adopt 
sea-level datum. 

There is shown below the information given on a card issued by 
the municipal engineers of the city of New York. It was prepared 
by the special committee on datum planes. It gives a comparison of 
the various datum planes in use in the city of New York. 



+2.( 



MEAN SEA-LEVEL DATUM FOR ELEVATIONS. 7 

THE MUNICIPAL ENGINEERS OF THE CITY OF NEW YORK. 

COMPARISON OF DATUM PLANES. 

— Richmond high wafer datura +3.192. 

— City datum or public works datum of Manhattan. Highways and sewers. Pennsylvania R. R. N. Y. Central R. R. +2.750 



Public Service Commission at Produce Exchange +2.653. ^, Queens Borough datum. Long Island City datum +2.725. 



Brooklyn Highway Bureau datum. Topographical Bureau datum +2.547. ^ Bronx Borough or Highway datum +2.608. 

U. S. Navy Yard datum. Brooklyn Water Supply +1.680. Brooklyn Sewer Bureau +1.678. Bridge Department +1.677. 



Standard datum. Mean sea level at Sandy Hook. U. S. Coast and Geodetic Survey datnn 



Board of Estimate and Apportionment datum. Board of Water Supply datum. 
Croten datum, at Jerome Avenue and McLean Avenue —0.785. 

Dock Department datum. Mean low water at the Battery —2.103. 

For history of above datum planes see Proceedings of Municipal Engineers for 1915. — 
Prepared by the Special Committee on Datum Planes November, 1916. 

• It is evident that in the city of New York there must be much 
confusion resulting from the use of so many datums, and it is pos- 
sible that the confusion in the elevations and the datums may involve 
the city in much extra expense on engineering work, due to erroi-s 
which must inevitably be made in interpreting the leveling data. 

Conditions in the city of Cincinnati in regard to elevations were so 
unsatisfactory that, in August, 1913, the council of that city adopted 
by ordinance mean s-ea level as the official datum for all city survey- 
ing and engineering operations. Before the adoption of this datum 
each of the various sections of Cincinnati which had been an inde- 
pendent town had its own datum for levels, and there was no official 
connection of the various systems of elevations. 

The city engineer of Birmingham informed the Coast and Geodetic 
Survey that mean sea level had been adopted as the official datum for 
that city. He said that Birmingham was made up of 13 municipali- 
ties, which were consolidated into one city government. At the time 
of the consolidation each of these municipalities had its own datum, 
and, owing to the fact that the city is about 14 miles long and 5 or 6 
miles wide, it would have been a considerable expense to the city 
after the consolidation to undertake to harmonize all of these datum 
planes. 

The engineer of the department of improvements and parks of 
the city and count}^ of Denver replied that the city datum for Denver 



8 UNITED STATES COAST AND GEODETIC SURVEY. 

was not referred to the sea in an^^ way. He closed his letter with 
the statement: 

There is, so far, no sentiment in favor of changing the old datum to that of 
sea level. Personally, I am in favor of doing whatever is necessary to bring 
about a change to the end that the official datum of every city in the country 
^vili refer to the sea. 

The cit}^ engineer of Memphis T\^rote, in part, as follows : 
I regret to advise that years ago an arbitrary datum was adopted here and 
that all of our city w^ork is based on this datum. It has no relation and no 
meaning whatsoever. However, our records at the present time comprise prob- 
ably 10,000 profiles and over 500,000 individual elevations, which would involve 
us in an enormous expense, with very serious chances of error, if we should 
try to change them. Personally, I should like to see them changed, but I see 
no chance of getting an appropriation for the work, and if I did have it the 
job would be a staggering one. 

The experience of the city of Memphis is what may be expected 
in any city that ma}^ adopt a datum not based on sea level. It is a 
warning to cities which have not yet adopted official datums that 
mean sea level should be the one selected. 

A letter was received from the assistant engineer of streets of 
Trenton, N. J., which read in part as follows: 

So far as our experience has taught us there can be no question as to the 
desirability of a universal datum plane, and I think there can be no doubt 
in the minds of engineers engaged in municipal work that mean sea level is 
the only logical datum plane to adopt. 

In your advocacy of an extension of such bench marks you deserve the sup- 
port and cooperation of every engineer in the country. 

That it is necessary to have precise leveling extended into areas 
where such control is not now available is clearly indicated by the 
data furnished by the city engineer of Salt Lake City. The only 
elevations available in Utah previous to about 15 years ago Avere 
from leveling by railroads, and that leveling was done for the imme- 
diate control of railroad construction rather than to carry absolute 
values with great accuracy. His letter contained the f olloAving : 

Below please find list of the different sea-level datum lines used in Salt Lake 
City. The city's datum being the lowest, I am calling it zero : 

Feet. 

Salt Lake City corporation 0.00 

United States Weather Bureau 23. 28 

Oregon Short Line Railroad 1 ^^ 

United States Coast and Geodetic Survey J 

Denver & Rio Grande Railroad 28. 42 

Frederick Law Olmstead, an authority on cit}^ planning, spoke 
of the need of a single datum in his report of the Pittsburg Civic 
Commission, which is entitled, "Pittsburg main thoroughfares and 
the downtown district," which appeared in December, 1910. In 
Part ITT, under the heading " Surveys and a city plan/' lie spoke of 
the need for surveys. One of the objects which he thought should 



MEAN SEA-LEVEL DATUM FOR ELEVATIONS. 9 

be secured is an accurate framework of reference points, including 
(1) the gradual systematic setting of street monuments throughout 
the city to serve as reference points for the definite determination of 
street locations and for all public and private local surveys; (2) the 
accurate determination of the locations and elevations of these and 
other monuments and bench marks in reference to a single general 
system of coordinates and in reference to the United States Govern- 
ment bench marks ; and (3) as a means of accomplishing these ends an 
accurate geodetic triangulation of the district, supplemented by the 
necessary precise traverse work and precise leveling all fully checked 
and compensated for errors. 

It will be seen from the preceding quotations and statements that 
city engineers in general are in favor of mean sea level as the datum 
for their elevations, but many of them hesitate at present to advo- 
cate a change from the arbitrarj^ datums on account of the expense 
involved. It is reasonably certain, however, that each city will 
eventually have to make a change, in order that the confusion inci- 
dent to the presence of many datums in the city and in the contiguous 
territory may be eliminated. 

As previously stated, the chief engineer of each of the States of 
the Union was requested by the Coast and Geodetic Survey to in- 
form this Office as to whether mean sea level was the datum used on 
official work in the State and whether the use of arbitrary datums 
by the various political and private organizations in the State re- 
tarded its development. 

In nearly all cases the State engineers answered that they are 
using mean sea-level datum on engineering work wherever it is prac- 
ticable to do so, and in most cases they expressed a desire that precise 
leveling, with elevations based on mean sea level, should be extended 
over the country as rapidly as possible, in order that mean sea level 
may be available to public and private engineers and surveyors. 
There are given below extracts from some of the letters received : 

The State engineer of Oklahoma wrote, in part : 

Replying to your letter, will say that this department is using sea- level datum 
on all of its work. The same datum is used in almost all of the cities of the 
State. I do not believe that any particular trouble is occasioned by the use of 
private or assumed datum planes, owing to the fact that we are so well fixed 
with the elevations all through the State that elevations may be reduced to 
sea level when the same may be needed. 

The State reclamation engineer of Texas said that his department 
constantly makes use of the bench marks established by the Govern- 
ment and that all of his work is based upon mean sea level. 

The State engineer of Wyoming said that he was heartily in ac- 
cord with the views of this Office relative to a standard datum for all 
elevations connected with surveying work throughout the United 
89759°— 17 2 



10 UNITED STATES COAST AND GEODETIC SURVEY. 

States. The surveys made under his supervision are, whenever pos- 
sible, based on elevations referred to mean sea level. In his opinion 
the standardization of all elevations and placing them on the same 
datum would be of great value to the engineering profession through- 
out the country. 

A letter received from the road engineer of the Iowa State High- 
way Commission read as follows : 

Replying to your letter of December 14, we would say that in highway work 
the county engineers are using the sea-level datum for all surveys wherever 
bench marks referred to such datum are available. We are unable to say 
just what percentage of the counties have such bench marks available. 

It would be a very great convenience to us if all of the surveys were referred 
to sea-level datum, as in a few years we will possibly want to prepare a topo- 
graphical map of the State, and if all the surveys were referred to one datum 
it would be unnecessary to reduce these various surveys to a common base. 

We are unable to state to which extent cities and towns are using the sea- 
level datum, but we think it is not very general except, possibly, in the cities 
and towns along the Mississippi or Missouri Rivers. 

The State engineer of New Mexico expressed the hope that some 
organization would take hold of the matter of the adoption of a 
single datum and try to persuade all engineers in his State to adopt 
mean sea-level datum in order to avoid confusion which is occasioned 
b}^ the use of a number of datums. He closed his letter as follows : 

This day (Dec. 27, 1916) there is being held at El Paso a tentative-plan 
meeting, calling all the engineers in New Mexico, Arizona, and Texas to 
organize a southwestern engineering society, and I feel that an organization 
of this kind, as soon as it is established and in working order, can do a great 
deal of good along this line of work. I will take it upon myself, after the 
organization of the society, to bring this particular subject before it. 

The chief engineer of Pennsylvania wrote that all the district 
engineers used mean sea level as the datum for their elevations and 
that his reports indicated that the majority of the city engineers 
also used mean sea level, but that the cities of York, Philadelphia, 
and Pittsburgh were using arbitrary datums. He expressed the 
opinion that there is no question but that in time it would be a gTeat 
help if all leveling could be based on one datum. 

The State engineer of South Dakota wrote that in all of the irri- 
gation, drainage, road, and other surveys that had been conducted 
under him mean sea level had been used as a datum for elevations. 

The engineer of the State of Kansas, in replying to the letter from 
the Survey, stated that — 

In so far as I have any information in the matter the various engineering 
projects of the State are based on various arbitrary datums. This condition 
necessarily causes much trouble in many instances. The most recent example 
I now have in mind is in connection with our investigation of flood conditions 
here in Kansas. Some of the most important data in this connection are those 
in the possession of the railreads, and in order to make them available it 



MEAISr SEA- LEVEL DATUM FOR ELEVATIONS. 11 

would probably be necessary to make maay adjustments in the various datums 
employed. Had all elevations been based on mean sea level, this trouble would, 
of course, have been avoided. 

The State engineer of Oregon wrote that in connection with the 
State's irrigation and highway work his department endeavored, 
wherever possible, to base its surveys on mean sea-level datum. He 
stated also that he found the bench marks of the United States Coast 
and Geodetic Survey and the United States Geological Survey of 
great benefit, as all surveys based upon them are on the same datum, 
and when connected form a uniform network over the State. 

This is a very important point brought out by the State engineer 
of Oregon, for it is where new surveys must be connected with other 
surveys that great confusion arises unless all are based upon the 
single datum for elevations. If there were to be only one survey 
in a restricted area, and that survey would never have to be joined 
to any others, it would be a matter of indifference as to whether one 
datum or another were used for elevations. 

The State engineer of Minnesota stated that he had not been able 
to use mean sea level throughout the State, but that as a general 
thing an arbitrary datum had been adopted ineach county; and, in 
fact, in each of several counties more than one arbitrary datum had 
been adopted. The reason for this condition was the lack of bench 
marks in his State. He closed his letter with this statement : 

We agree with you that it would be very valuable to the State if a system of 
levels could be established, and believe that such will need to be done in the 
near future in order to correlate the drainage, highway, and other engineering 
work in the State. 

The State highway engineer of Alabama, in a letter to this Office, 
stated that wherever possible his department based the elevations of 
their road work upon mean sea level. He expressed the wish that a 
sufficient amount of leveling might be done in his State to enable all 
of the road work to be based upon mean sea level for elevations. 

The deputy State engineer of New York informed this Office that 
the engineering department of that State has, since 1898, used mean 
sea level in all of its work. Previous to that time, elevations were 
upon a different datum for each of the three divisions of the New 
York State canals, those divisions having their headquarters at 
Albany, Syracuse, and Rochester. He said that several hundred en- 
gineers, who had been employed by his department, but were no 
longer connected with it on account of the completion of the barge 
canal, are now employed by municipalities and large corporations, or 
are in private practice. As they are familiar with the sea-level 
datum they are gradually changing the datums in different localities 
to that one. They are having considerable influence toward securing 
the general adoption of mean sea-level datum. 



12 UNITED STATES COAST AND GEODETIC SURVEY. 

The assistant superintendent of the Department of Public Works 
of the State of Ohio expressed the hope that mean sea level would 
be adopted throughout the entire country as the datum for elevations. 
His letter read, in part, as follows : 

This department lias spent some time and considerable money in standardiz- 
ing our levels over the public works of the State and we are now using United 
States datum (sea-level datum). 

The writer had occasion to be called in consultation on certain proposed im- 
provements and the county engineer used a datum of his own selection. The 
city engineer selected a different datum, v^hile the writer used in his calcula- 
tions the United States datum. The result, as you can very readily see, was 
confusion which made necessary an extra amount of work to bring the various 
arbitrary datums to the same standard. 

The chairman of the Public Utilities Commission of Maine stated 
in his reply that — 

We are thoroughly in accord with your ideas as to the confusion resulting 
from the use of arbitrary datums on projects requiring the determination of 
elevations and this commission has endeavored, in so far as it has been able 
to do so, to extend the use of mean sea-level datum on State, municipal, and 
private engineering works in Maine. 

He closed his letter with the request for the elevations of bench 
marks established on a line of precise levels extended across the 
State of Maine by a. party of the United States Coast and Geodetic 
Survey in 1916. He believed that such data as may be available could 
be advantageously tabulated and published in the volume of the 
annual report of the Public Utilities Commission relating to topog- 
raphy, geology, and water resources. 

It might be well if the various States were to assist the Federal 
Bureaus in placing the leveling and other engineering data before the 
engineers of the States. This could be done very well by having the 
necessary data appear in the annual reports of the State engineers 
and of public utility commissions. 

The various railroads of the country are vitally interested in the 
adoption of mean sea level as the sole datum for elevations in the 
country, for each of a number of railroads traverses the territory of 
several States and of innumerable cities and towns. There is neces- 
sarily a great deal of confusion in elevations between the railroads 
and the various municipalities and political units through which the 
roads pass if each unit has its own datum. 

The Interstate Commerce Commission directed the various rail- 
roads of the country to shoAv on their profiles the equations neces- 
sary to reduce elevations to sea-level datum or to have the profiles 
based upon mean sea level. This was for the valuation work under- 
taken by the commission. The result of this requirement has been 
that many railroads changed from arbitrary datums to the mean sea- 
level datum, although probably most of the roads of the country had 
previously adopted mean sea level as their datum. It may be inter- 



MEAN SEA- LEVEL DATUM FOR ELEVATIONS. 13 

esting to note that the Board of Railway Commissioners of Canada 
has directed the railroads of the Dominion to submit all informa- 
tion in connection with elevations and profiles on mean sea-level 
datmn. 

It will be of interest and value to learn the opinion of a number 
of the chief engineers of the various railroads of the Country with 
regard to mean sea-level datum. To a letter sent out to them by 
the United States Coast and Geodetic Survey a number of replies 
were received. The Survey's letter requested information as to 
whether or not mean sea level was used by the railroads; if not, what 
datum was used; and if arbitrary datums were used in the territory 
traversed by the roads, whether they were a handicap to the develop- 
ment of the territory. 

There are given below the substance of some of the letters and 
actual quotations from others. 

The assistant chief engineer of the Minneapolis, St. Paul & Sault 
Ste. Marie Railway Co. stated that his road was using sea-level 
datum on its entire sj^stem, except on the Chicago division, but that, 
as fast as possible, that division was being reduced to mean sea-level 
datum. He said in part: 

The use of various arbitrary datums by States, cities, counties, and private 
organizations along our line has not been a very serious matter, except tlmt 
it requires more labor and particular care to convert their datums to the one 
which we use. There is always a possibility of error in this conversion of 
datums that would be eliminated by standardizing sea-level datum. 

The chief engineer of the Duluth & Iron Range Railroad Co. said : 
Many other organizations in our vicinity use either an assumed datum or a 

datura which is supposed to correspond to the mean low water of Lake Superior. 

The discrepancy between the various datums is often confusing, and I have 

known cases where the confusion resulted in mistakes in construction which 

were expensive. 

The chief engineer of the Chicago Great Western Railroad stated 
that his road used sea-level datum for all of its elevations in connec- 
tion with maps and profiles. He added : 

We consider the use of arbitrary datums by States, cities, and counties as 
causing considerable inconvenience. Quite frequently it is necessary to com- 
pare [our] levels with local work, and where elevations are not on sea-level 
datum it results in confusion and more or less misunderstanding. 

The chief engineer of the Philadelphia & Reading Railway Co. 
wrote in part : 

Our system for some years back has used mean tide at Sandy Hook for its 
datum, and we believe that it is the only reasonable one for such purposes. In 
the city of Philadelpliia, where an arbitrary datum is used, we have to make 
our plans conform to the Philadelphia city datum, in so far as such plans 
affect city improvements. 

It is distinctly a serious matter to have different localities using different 
datums, and we shall be glad to see any movement toward the abolishment of 
any datums which are not based on mean sea level. 



14 UN'ITED STATES COAST AND GEODETIC SURVEY. 

The chief engineer of the Chicago & North Western Eailway said : 
I thoroughly agree with you that this precise leveling is essential in the 
surveying and engineering work done in this country by various public and 
private agencies. 

We endeavor to base our elevations upon mean sea level wherever possible, 
but find that the use of various datums by cities, counties, and States results 
in considerable confusion and arguments. I am of the opinion that if we had 
but one datum all of our work would be more easily coordinated and would 
result in less confusion and waste than at present. 

The chief engineer of the Chicago, Rock Island & Pacific Railway 
expressed the opinion that the establishment of arbitrary datums 
by States, cities, counties, and private organizations should be dis- 
couraged as much as possible, as they cause a great deal of confusion. 

The chief engineer of maintenance of way and structures, lines 
east, of the Southern Railway system said, in part : 

I am glad to advise that for some years past on this railway we have had all 
our surveys tied into sea-level datum. We have found that the presence of 
various datums leads to much confusion and waste. 

The chief engineer of the Western Maryland Railway Co. said : 

We have had and still encounter trouble in avoiding errors due to the differ- 
ent datums used by adjacent railroads, various cities, counties, and private 
organizations. We are heartily in favor of the establishment of an authorita- 
tive datum for use and adoption by all. 

The engineer of the Chicago, Peoria & St. Louis Railway Co. 
wrote that — 

We are endeavoring to reduce the various arbitrary datums used in the con- 
struction of this line to sea-level datum. We do find that considerable incon- 
venience is occasioned by the use of arbitrary datums. Inasmuch as we are 
brought in touch with various drainage projects along the line we feel that 
some common datum should be used. 

The chief engineer of the Missouri Pacific Railway wrote as 
follows : 

It is very desirable, though not absolutely essential, to use one datum plane 
for all engineering elevations, as with conditions as at present existing there 
is a great deal of confusion and time lost in looking up proper equations to 
change from one datum plane to another. 

In getting rough approximations of the discharge of streams it is necessary 
to know the approximate slope, and to get this it is necessary to know the 
elevations of crossings of the river at different points on its course. Where 
elevations of these crossings are referred to different datums it is fre- 
quently impossible to get more than a very rough approximation of the differ- 
ence of elevations, which results in a corresponding approximation of the dis- 
charge. This also very frequently happens in connection with drainage work. 

The use of various arbitrary datums by States, counties, cities, and private 
organizations is becoming more and more a serious problem, for the reason 
that it requires considerable research or investigation to determine whether 
the elevations used are referred to sea level or other datum planes and then 
to ascertain the correct equations. 



MEAN SEA-LEVEL DATUM FOR ELEVATIONS. 15 

I do not know of any one thing which the Coast Survey has undertaken 
which will be of greater benefit to the engineering profession of the country 
at large, in so far as all engineering operations are concerned — and by this 
one can almost say all industrial development of the country — than to promote 
and secure the adoption of mean sea level as the datum for all elevations. 

The chief engineer of the Illinois Central Kailroad Co. informed 
this Office that his road i;ises mean sea level as the datum for its 
elevations. He concluded by saying: 

The various datum planes used by cities and surveyors along the lines of 
this company cause, in many cases, confusion and inconvenience in connection 
with the working up of plans and the correlating of them to local surveys. It 
would be of great benefit if, as you suggest, a single datum plane were in use 
all over the United States, and presumably this will be in effect some day, 
but the time will be greatly advanced through the establishment by the United 
States Coast and Geodetic Survey of bench marks throughout the country. 

The chief engineer of the Kansas City Southern Railway Co. said 
he believed that if a universal sea-level datum could be adopted by 
all State, county, and city organizations it would be of great benefit, 
not only to the railroads but to other industrial as well as private 
organizations. He heartily indorses any movement that would bring 
about this plan. 

The chief engineer of the Lehigh Valley Railroad Co. said in part : 

I agree with you that it would be a very great benefit If the country should 
eventually have but one datum, in order that all engineering and surveying 
work may be easily coordinated. This would save considerable annoyance and 
many errors. 

The chief engineer of the Hoclring Valley Railway Co. said that 
all of the elevations of his road are referred to sea-level datum but 
that, as far as he knew, none of the towns or cities on his line used 
that datum. He said that the idea that all levels should be referred 
to sea-level datum is an excellent one and that it would facilitate 
matters if the whole country would adopt this datum for all of its 
leveling. 

The chief engineer of the Delaware, Lackawanna & Western Rail- 
road Co. said: 

There is no question in our work but that the variation in the data is confus- 
ing, and it certainly would be not only to the railroad company's interest but 
to the interest of the municipalities, boroughs, etc., along the line to have a 
uniform datum. 

The chief engineer of the Michigan Central Railroad Co. is using 
mean sea level on that road as the datum for all elevations. He adds: 

I believe that the use by States and counties and by private organizations of 
datums different from the sea level one is a great disadvantage, especially where 
the railroads are requested to do work in connection with them, such as build- 
ing sidetracks, etc. When the elevations of floors and other portions of a 
building are given on an arbitrary datum and the railroad w^ork is done on the 



16 UNITED STATES COAST Al^D GEODETIC SURVEY. 

sea-level datum, there is always very great chance of error in relating one 
datum to the other. 

The chief engineer of the Chicago & Alton Railroad Co. stated that 
it is unfortunate that the municipalities have not, like the railroads, 
adopted the mean sea level. As an illustration he stated that almost 
every day situations occur in Chicago where elevations are referred 
to city datum ; that is, the average elevation of Lake Michigan. This 
produces confusion, as it is necessary to consider the relation of the 
arbitrary datums with reference to mean sea level, which is almost 
universally used as the datum by railroads, geological surveys, etc. 
He added: 

Any departure from the Government datum produces confusion and often- 
times embarrassing situations. I have had such experience in the city of 
Cleveland and in the city of Pittsburgh, where for many years no datum plane 
of any sort existed that was reliable and properly referenced. 

The chief engineer of the Pennsylvania Eailroad Co. informed the 
Survey that all construction on his road was based upon elevations 
on the sea-level datum, with the exception of some few cases where 
his work joined with that of cities, when it was necessary to have 
plans based upon the datums adopted by the municipalities. He 
expressed himself as being heartily in favor of reducing all eleva- 
tions in the country to the mean sea-level datum. 

The chief engineer of the Boston & Albany Railroad wrote in part 
as follows: 

We have found Government precise leveling of the greatest service to us in 
connection with our heavy reconstruction on the Boston & Albany Railroad. 
We are running altogether on the Government datum, and I quite agree with 
you that the whole country should adopt it if at all possible. 

The various datums at present in use in cities and towns cause much con- 
fusion and waste of time in equating between them. For instance, in our 
work in the city of Boston, with which the city work comes in contact, we 
have to run everything on sea-level datum and also on the city of Boston 
datum, and similar conditions obtain in Worcester and Springfield. 

I have been endeavoring, as far as possible, to get the various town and city 
engineers along our road to adopt the sea-level datum, and several of them are 
now using it. 

The chief engineer of the Los Angeles & Salt Lake Railroad Co. 
wrote that — 

A book can be written setting forth the value of precise levels and the 
disadvantages of assumed levels. Therefore, I think it only necessary to say 
that we use your levels wherever we find them, and our regret is that your 
work is not now further advanced. We are in hearty sympathy with your 
work and hope that you will be able to continue it in a broad way. 

The chief engineer of the St. Louis-San Francisco Railway Co. 
informed the Survey that all the profiles of his road that are now 



MEAX SEA-LEYEL DATUM FOR ELEVATIONS. IT 

being prepared, or that have been prepared for some time past, are 
based on sea-level datum, and that he considers it a serious proposi- 
tion to have various arbitrary datmns by States, counties, cities, etc. 
He said that serious difficulties were encountered by his road as a 
result of various datums in connection T\^ith drainage matters, grade 
separation, and development work. 

The chief engineer of the Wisconsin & Northern Railroad Co. said, 
in part: 

As a general proposition tliere can be no question as to the great desirability 
of having nil surveys and benches referred to sea-level datum, and in other 
surveys upon which I haA^e been engaged in this territory for interurban lines, 
and, to a minor extent, water-power development, I have gone to some pains 
to establish such datum. While from my own experience I can say but little 
as to the bearing of this question upon industrial development, I can say 
without hesitation that the matter is an important one and will become in- 
creasingly so as the country becomes more highly developed. I would add 
from observation that from the tremendous expansion now beginning in 
permanent road construction, the providing of such base lines of precise 
leveling as you mention at the earliest practicable date would be of the greatest 
importance and benefit. 

The chief engineer of the Oregon Short Line Eailroad Co. an- 
nounced that his road is using mean sea -level datum for all of its 
elevations. He said that he found the results of the United States 
Coast and Geodetic Survey leveling invaluable for his use in con- 
nection Avith location and maintenance Avork. He expressed the 
belief that, if engineers generally could realize the saving in time and 
lessening in confusion which would result from the use of the mean 
sea-level datum, they would eliminate the various independent 
datums and adopt the standard sea-level datum. 

The chief engineer of the Northern Pacific Railway Co. replied that 
there is a great deal of confusion at present caused by the various 
datums used for level Avork by different railroad companies, cities, 
and private organizations. He also said that the Northern Pacific is 
using sea-level datum, but that there is confusion caused by the fact 
that sea-level datum, as used by other organizations, had different 
elevations. He expressed the opinion that engineering Avork Avould 
be greatly facilitated if it could be based on the same datum fur all 
the States. 

This is another instance where eleA^ations, supposedly based on 
mean sea level, are in error because of the lack of precise leveling 
elevations before the detailed leveling Avas run. This is an argument 
for the extension of the precise level net into the areas Avhich now 
do not have this fundamental control. 



18 UlsriTED STATES COAST AXD GEODETIC SURVEY. 

The chief engineer of the Toledo & Ohio Central Railway Co. 
approved of any mo^ ement to establish reliable bench marks, referred 
to sea level, over the territory of the United States as, in his opinion, 
it would be of great value to the engineering profession and to all 
industries w hich have engineers in their service. He added : 

In days gone by a great many surveys were made on our road and referred 
to any arbitrary datum that the man in charge might choose, with the result 
that we find it difficult and inconvenient many times to utilize properly, the 
results obtained from these old surveys. All the work we are now doing is 
referred to sea-level datum. 

The quotations contained herein from letters received from many 
of the most prominent engineers of the country prove conclusively, it 
is believed, that it would be far better for the country in its in- 
dustrial and engineering developments if there were used only one 
datum and if that datum were mean sea level. It is realized by the 
members of the Coast and Geodetic Survey that much of the con- 
fusion in datums which now exists is due to the fact that the precise 
level net of the United States was not extended in the past as rapidly 
as it should have been. It, of course, was impossible, or rather im- 
practicable, to extend a precise level net into areas through which 
railroads had not been run, for the expense would have been pro- 
hibitive. It may be that the Survey did not fully realize the neces- 
sity for having all engineering and surveying work on the same 
datum, but in recent j^ears it has been fully alive to the necessity of 
having a single datum for the entire country, and it is consequently 
extending its precise leveling net as rapidly as funds available will 
permit. 

To show how active the Survey has been in its precise leveling in 
recent years, it may be stated that in December, 1907, there were in 
the United States 24,000 miles of precise leveling which had been run 
b}^ the United States Coast and Geodetic Survey, the Corps of Engi- 
neers, United States Army, the United States Geological Survey, the 
United States Lake Survey, the Pennsylvania and the Baltimore & 
Ohio Railroads, together with the Mississippi and Missouri River 
Commissions. The amount of precise leveling in the country in De- 
cember, 1916, was 35,500 miles. It may be interesting to note that 
during the calendar year 1916 about 2,500 miles of precise leveling 
were added to the net by the Coast and Geodetic Survey. 

That the amount of precise leveling in the United States is entirely 
inadequate is shown in the following table which gives the amount of 
leveling in many of the countries of the world. This table also shows 
the amount of such leveling for each 100 square miles of area. We 
should double the amount of leveling in this country within the next 
few years. 



MEAN SEA-LEVEL DATUM FOR ELEVATIONS. 19 

l*EECisE Leveling in a Numueii of Countries. 



Country. 





Miles of 


.Vrea. 


precise 




leveling. 


Square miles. 




2,970,000 


35,500 


591, 000 


20 


121,000 


12,804 


241,000 


13,129 


207,000 


7,284 


209,000 


33, 651 


111,000 


4,603 


170,000 


9,129 


1,767,000 


17,301 



Miles of 

precise 

leveling per 

100 square 

rciles of 

area. 



United States 

Alaska 

British Isles 

Austria-Hungary . 

France 

German}^ 

Italy 

Japan 

India 



L2 
.0 

10. « 
5.4 
3.5 

16.0 
4.2 
5.2 
1.0 



While it is of value to the Xation for various organizations and 
individuals to adopt and use mean sea-level datum for their eleva- 
tions, the countr3r will benefit still more if each organization doing 
extensive leveling will publish in pamphlet form the elevations and 
descriptions of the bench marks they may establish in order that 
other organizations and individuals may properly coordinate their 
levels. Engineers are urged also to use substantial bench marks in 
order that future work may be benefited by their preservation. In 
this connection it may be interesting to quote from a letter which 
was sent to the Engineering Eecord by F. D. Yeaton, of Oak Har- 
bor, 111. This letter appeared in the issue of May 20, 1916, and is 
entitled: " Surveys and bench marks — more permanence needed." It 
reads as follows: 

SiE : I would like to suggest a more general use of sea-level datum and refer- 
ence ties to public land lines for all surveys, the lack of v^'hich will generally 
be found to be weak points in many surveys. The too frequent practice of 
using assumed bench marks, such as spikes in trees, or tops of curbs, should 
be discontinued wherever practicable. Reference points, such as stakes and 
marks opposite center of structures, are often used instead of township and 
section lines. It is only a question of a few years before assumed bench marks 
and reference points will be destroyed, and the surveys will be practically 
valueless for future use. 

Recently I desired records of high-water marks along a certain strip of land 
to use in establishing a high-water plane. Several dozen surveys, which had 
been made for permanent bridge work and which contained high-water records, 
were obtained from the files. As is often the case, the surveys had been made 
from assumed bench marks. The connecting links were missing and the sur- 
veys were valueless for my purpose. 

One finds many maps, profiles, and topographical surveys on file in engineer- 
ing offices bearing practically no direct relation to each other. Engineers have 
had occasion in valuation work, and in lawsuits involving surveys, to handle 
maps and profiles the value of which would have been intrinsic if only some 
relation between the maps and the profiles could have been established. The 
engineering departments of both small and large corporations are more or less 
at fault in the matter of allowing surveys to be made and filed which are of 
practically no future value. 



20 UNITED STATES COAST A^^D GEODETIC SURVEY. 

The Federul Government has estab]islie<l sea-level bench marks and perma- 
nent hind lines in many parts of the country, and their use shouhl become more 
general in surveys of all kinds. The more general use of sea-level datum and 
land-line ties for surveys will aid greatly in reducing the duplication of field 
surveys, and will tend toward inaugurating a more permanent and economical 
policy of making and filing surveys. 

In the October 13, 1916, copy of Science there is a short article 
entitled " Expedite the map." It announced that a committee to 
expedite the completion of the topographic map of the United States 
had been formed, on the invitation of the well-known geographer 
and geologist, Prof. W. M. Davis, of Harvard University. Prof. 
Davis, the writer of the article in Science, made the statement : 

Every industry, art, and science v\^hich demands a knowledge of the lay of 
the land is benefited by good maps of the area in which work is carried on. 
The general location of railways and highways, the planning of water supplies, 
irrigation, and drainage projects, the prosecution of geological, soil, and forest 
purveys, the development of water powers, and the installation of electric 
transmission lines, the promotion of large-scale realty transactions such as are 
common in the less settled parts of the country, are all aided immensely if 
good topographic maps of their areas are available, and they are correspond- 
ingly embarrassed if such maps are wanting. Practical men who have had ex- 
perience in mapped and in unmapped areas can testify to the ease and the 
difficulty of work in the two cases. 

This is admirably stated and is convincing in showing the neces- 
sity for accurate topographic maps in the country. Engineers will 
realize that such maps can not be accurate and can not be of the 
greatest value unless each map or section of a map has its elevations 
and contours referred to a common datum. 

CONCLUSION. 

The Survey, whose obligation it is to extend the precise leveling 
net over the country for the use of Federal, State, city, and other 
engineering, surveying, and mapping work, feels that the expressions 
of opinion of the leading engineers of the country point to only one 
conclusion. This is that the Federal Government should provide the 
fundamental elevations in sufficient number that the various Federal 
engineering and surveying organizations and the smaller political 
units such as States, counties, and cities, as Avell as private organiza- 
tions and individuals, may have available fundamental elevations 
upon which to start leveling, precise or otherwise, for detailed oper- 
ations. 

The amount of precise leveling which should be done by the Federal 
Government can not be foretold. It must depend upon the needs of 
the various organizations and individuals using the results. After a 
certain development of the precise level net which appears now to be 
absolutely necessar}^, the rapidity with which further extensions are 



MEAX SEA-LEVEL DATUM FOR ELEVATIONS. 21 

made should depend upon the development of the country. But such 
further extensions should precede rather than follow such develop- 
ment as is proved by the mifortunate condition of affairs in much of 
our engineering and surveying work, due to lack of precise elevations 
in the past, when such work was inaugurated. 

With the increased demands for accurate topographic maps of the 
country, the wonderful extension of our good-roads movement, the 
extension of the railroads, and the development of river, irrigation, 
and drainage projects, the precise leveling of the country should be 
carried in the near future into many of the large areas now having 
little or no accurate leveling. The further conclusion may be drawn 
that it will be best for the efficiency of the country as a whole that all 
new leveling, by the various organizations and individuals engaged 
upon engineering and surveying work, be placed upon mean sea-level 
datum, wherever this is practicable, and also that as far as possible 
existing leveling referred to arbitrar}^ datums should be changed to 
sea-level datum. 

It is hoped that as a step toward the industrial preparedness of 
our Xation the engineering press, the Xational. State, and city engi- 
neering societies and associations, and engineering organizations and 
individuals of the country will take an active part in furthering the 
use of mean sea level as the datum for elevations. 

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